The proposed study on recruitment, adherence and retention in clinical trials among injection drug users (IDUs) and others is a study to be conducted simultaneously with the AIDS Clinical Trials Unit at Yale University. The long-term objective is to improve recruitment, adherence and retention in clinical trials particularly among those traditionally under-represented in clinical trials: IDUs, women, and minorities. The specific aims of this study include: (1) To determine if injection drug use and sociodemographic factors (sex, race) influence participation in clinical trials for HIV-related drugs; (2) To determine what factors influence successful recruitment in a clinical trial, examining the relative importance of several classes of variables - type of clinical trial, HIV-related medical status, and behavioral factors; (3) To develop a psychosocial profile of clinical trial participants, including knowledge, attitudes and behavior associated with recruitment, adherence and retention in clinical trials. And, in an exploratory way, to investigate psychosocial and attitudinal factors among persons who decline participation in a clinical trial; (4) Prospectively, to determine which of the above sociodemographic, medical, behavioral or psychosocial factors (and combinations of factors) predict adherence and retention in clinical trials among those enrolled; (5) If injection drug use, in and of itself, is an important predictor, to examine what factors differentially predict recruitment, adherence and retention for IDUs and non-IDUs; and, (6) To examine whether participation in clinical trials, per se, influences health-relevant attitudes, behavior, and outcomes. Data will be collected from HIV/AIDS patients who agree (experimental group) and disagree (comparison group) to participate in clinical trials. Biomedical, virology and immune data will be gathered from existing medical records for all subjects (N=500-600). In addition, interviews will be conducted by a trained clinical interviewer: 1 interview with a select group of comparison group members (n=200), and 3 interviews over the course of the clinical trial for the experimental group members (n = 200). All experimental group members will be interviewed at enrollment and 3 months post-enrollment to enable comparative prospective analysis; the timing of a third interview is dependent on type of trial (phase I vs. II/III) and completion versus termination of trial. A series of hierarchical logistic regression models will be used to analyze these data. This research will take place in New Haven, CT, where two-thirds of AIDS cases are associated with injection drug use. The size of the city, the number of cases of HIV/AIDS, and the consolidated nature of the healthcare system enables a population-based study of recruitment, adherence and retention in clinical trials.